Upconverted light emission and switching in dye-doped polymer waveguides

We report the results of study of upconverted emission in the band 520 to 600 nm from waveguides made of poly(methyl methacrylate) (PMMA) doped with laser dye 4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H-pyran known as DCM. The emission could be excited using CW laser pumping within the range 630 nm to 800 nm with intensity below 1 kW/cm(2). The excitation mechanism, instead of the two-photon absorption, more likely involves exciton-like lokalized states below the S1 singlet state. These localized states, being excited by low energy photons can assist in populating upper singlet states according to the scheme of the excited state absorption. We also pay special attention to material photobleaching that accompanies upconverted emission. This effect leads to refractive index decrease at the wavelength of the pump. Computer simulations based on numerical solutions of nonlinear propagation equation as well as experiments show that photobleaching leads to irreversible branching of optical pump beam that propagates through a dye-doped polymer waveguide.